1. Field of the Invention
The present invention relates generally to lenses for optical waveguide fibers, and particularly to an apparatus and method of making lenses for optical waveguide fibers.
2. Technical Background
Advances in optical communications have generated significant need for optical components that involve light being transmitted to or from an optical fiber through free-space to interact with or pass through one or more optical device. A wide variety of passive and active optical devices exist, some simple examples including thin-film filters or birefringent elements, and some of the more complex being large scale three-dimensional switch fabrics. Other uses for free-space optical components include injecting light from a laser diode into an optical fiber, transmitting light through free-space from one optical fiber to another (such as an amplifier fiber) or projecting light from an optical fiber to a detector.
In optical components utilizing free-space transmission of light (sometimes called micro-optic components), the light beam is often either expanded and collimated into approximately parallel rays from the exposed end of an optical fiber, or conversely focused from an expanded beam into a narrower beam capable of being injected into the end of the optical fiber at a desired angle of incidence. While other functions may be performed on the light beam exiting or entering an optical fiber, collimating and focusing are the functions that are most commonly encountered in micro-optic components.
In order to accomplish the collimating or focusing functions within the specifications required for optical communications, cylindrically-shaped gradient-index (GRIN) lenses employing graduated radial refractive index profiles have become the most prevalent conventional alternative. However, commercially-available GRIN lenses are expensive, difficult to manufacture, and present certain disadvantages in assembling, aligning, and tuning the optical components.
Several other approaches to fabricating collimating or focusing lenses for optical components are known. Axial GRIN lenses, molded polymer and glass lenses having spherical and aspherical lens surfaces, composite or complex lens elements, optical fibers having integral lenses formed by processes such as thermal expansion or diffusion, and ball lenses are among the many alternatives.
Thus there exits a need for a method of making lower cost precision lenses for optical components.
One aspect of the invention is an apparatus for making a lens on the end of an optical waveguide fiber. The apparatus includes a laser, wherein the laser emits a laser beam. The apparatus further includes a beam expander disposed to receive the laser beam, whereby the beam expander increases the diameter of the laser beam, thereby producing an expanded laser beam. The apparatus further includes a first aperture disposed within the expanded laser beam, wherein the first aperture blocks a portion of the expanded laser beam, and a second aperture disposed within the expanded laser beam, wherein the second aperture blocks a portion of the expanded laser beam. The apparatus further includes a first mirror disposed in the path of the expanded laser beam wherein the first mirror redirects the expanded laser beam. The apparatus further includes a focusing mirror disposed to receive the expanded laser beam, wherein the focusing mirror focuses the expanded laser beam thereby forming a heat zone. The apparatus further includes a first positioner disposed to selectively position at least a portion of a lens preform within the heat zone, and a second positioned disposed to selectively position at least a portion of an optical waveguide fiber within the heat zone.
In another aspect, the present invention includes method for making a lens on the end of an optical waveguide fiber. The method includes the step of providing an optical waveguide fiber, the optical waveguide fiber having at least one end. The method further includes the steps of providing a lens preform and of coupling the lens preform to the at least one end, thereby forming a junction. The method further includes the steps of determining the volume of the lens to be formed, determining the length of the lens preform that corresponds to the determined volume and removing the portion of the lens preform that is in excess of the volume of the lens to be formed. The method further includes the step of forming the lens.
One advantage of the present invention is that it is a monolithic lens and fiber assembly.
Another advantage of the present invention is that only a single surface requiring an anti-reflective coating is produced.
Another advantage of the present invention is that it has lower polarization dispersion losses than gradient index (GRIN) lenses.
Another advantage of the present invention is that compared to ball lenses there are no micro cracks.
Another advantage is that the manufacturing costs of the present invention are lower than the manufacturing costs associated with either ball or GRIN lenses.
Another advantage of the present invention is that it may be used to make divergent beam lenses.
Another advantage of the present invention is that it may be used to make tightly focusing beam lenses.
Another advantage of the present invention is that it may be used to make collimating lenses.
Another advantage of the present invention is that it may be used to make lenses for efficiently coupling optical waveguide fibers to laser diodes.
Another advantage of the present invention is that the coating does not have to be removed from the optical waveguide fiber before forming the lens on the end of the optical waveguide fiber.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely illustrative of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operations of the invention.